Device for suppressing signal interference

ABSTRACT

A device for suppressing interference signals for a microprocessor evaluating a plurality of sensor signals on respective input lines coupled thereto. Each of the input lines is selectively coupled to a first resistance during a measurement interval and selectively coupled to a second resistance during an interval outside of the measurement interval.

FIELD OF THE INVENTION

The present invention relates to an electronic device.

BACKGROUND INFORMATION

A conventional electronic device is described in U.S. Pat. No.5,037,129. If sensor signals that are affected by severe interferingsignals must be processed in such a conventional device, undesiredinterference can occur, particularly during a conversion of the analogsensor signals into digital signals. These interferences are perceptibleas, for example, "crosstalk," the coupling-in of undesired interferingsignal components on adjacent lines or, for example, adjacent channelsof a multi-channel analog/digital converter (A/D converter).

SUMMARY OF THE INVENTION

The electronic device of the present invention allows particularlysimple and elegant suppression of undesired interfering pulses, so theoutput signal of a sensor to be processed as a desired measured signalis essentially further processed free from interference; in particular,it can be converted into a corresponding digital output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of the electronic device according to thepresent invention.

FIG. 2a shows a plot of an output signal of a sensor as a function oftime for the electronic device shown in FIG. 1.

FIG. 2b shows a plot of a resistance as a function of time for theelectronic device shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

An electronic device for controlling protective devices (e.g., an airbagsystem) for vehicle passengers, is shown, for example, as a blockdiagram in FIG. 1. The device includes an acceleration-sensitive sensor1, preferably a piezoelectric sensor whose output connection isconnected to a voltage divider R1, R2. The low end of voltage dividerR1, R2 is connected to the ground connection. In the block diagramshown, the tap of voltage divider R1, R2 is connected to an inputconnection 0 of a microcomputer 2 that includes a plurality of inputconnections. The plurality of input connections 0 through 7 ofmicrocomputer 2 are connected in time-multiplex fashion to the inputconnection of an A/D converter 30 contained in the microcomputer, whichconverts the analog output signals of sensor 1 into correspondingdigital signals. Each of the illustrated input connections 0 through 7can be switched with a corresponding input wiring, such as inputconnection 0. Consequently, a plurality of sensors 1 and a plurality ofvoltage dividers R1, R2 can be provided which are connected tocorresponding input connections of microcomputer 2. Microcomputer 2further comprises two reference-voltage connections 20, 21, to whichreference voltages can be applied. As an example, reference-voltageconnection 20 can be connected to the ground connection, while apredeterminable reference voltage can be applied to reference-voltageconnection 21. An output connection 22 of microcomputer 2 is connectedwith at least one airbag system 3 provided for passenger protection. Theoutput signal present at output connection 10 of sensor 1 is supplied tovoltage divider R1, R2 and scaled to the detection range of the A/Dconverter of microcomputer 2. This detection range is, for example, inthe voltage interval between 0 and 5 Volts. Thus, the actual measuringtask involved in detecting the output signal of sensor 1 is fulfilled.If, however, interfering voltages occur which are superimposed over theoutput signal of sensor 1 and are outside of the admissible measuringinterval, protective circuits in the input wiring of the A/D convertermust bear this additional stress. Usually, this is possible in currentlycommercially-available microcomputers without resulting in thedestruction of the input wiring. However, in most cases the response ofthe input wiring of an A/D channel, for example the channel indicated by0 in FIG. 1, which is provided for purposes of protection, cannotguarantee that measurements can be taken on the other channels, forexample channels 1 through 7, without interference. To assure extensivesuppression of interference even in this situation, the input connectionof the microcomputer that respectively leads to the A/D converter isconfigured such that it can be connected to two different potentialvalues. The assumption here is that the output signals of sensors 1 arerespectively scanned in time-multiplex or cyclical fashion so that theoutput signals detected during the scan time can be converted intodigital signals. The operating time can thus be divided into measurementphases and inactive phases. According to the present invention, it isprovided that, during the respective measuring phases, the respectiveinput connection of microcomputer 2 is connected to a first potential,and during the respective inactive phases it is connected to a potentialthat is different from the first. Thus, it is ensured that interferingpulses that occur at an input connection of microcomputer 2 during aninactive phase cannot interfere with adjacent signal channels. An inputconnection of a microcomputer is connected, particularly simply andpractically, to a respectively different potential in that it isconnected to a digital port of microcomputer 2. As shown in FIG. 1, forexample, input connection 0 of microcomputer 2 is additionally connectedto the digital port DO of microcomputer 2. The A/D inputs 0 through 7 ofmicrocomputer 2 are connected in time-multiplex fashion to the inputconnection of the A/D converter disposed in microcomputer 2 such thateach input channel 0 through 7 is connected to the input connection ofthe A/D converter for a predeterminable measurement time, for example 6microseconds. This measuring process is explained in conjunction withthe plots shown in FIGS. 2a and 2b. FIG. 2a shows, as an example, theoutput signal of sensor 1, namely the voltage U_(MESS1), as a functionof the time t. This output signal reaches A/D input 0 of microcomputer 2via voltage divider R1, R2, and is scanned and converted into acorresponding digital signal during a time interval T1, T2. As can beinferred from FIG. 2b, digital port DO of microcomputer 2 that isconnected to A/D output 0 during this time interval T1, T2 is actuatedsuch that it is in the tri-state, that is, a high-resistance state. Forexample, it represents a resistance R1, which is significantly greaterthan the resistance R0 assumed by digital port D0 of microcomputer 2outside of time interval T1, T2. Because of the relativelylow-resistance connection of A/D input 0 outside of time interval T1,T2, interfering pulses superimposed over the output signal of sensor 1cannot lead to crosstalk and interference of the measurements at theother A/D inputs.

In one embodiment of the present invention, resistances R1, R2 ofvoltage divider R1, R2 each have a value of, for example, 50 KΩ. It isfurther assumed that an interfering voltage of ±50 Volts is superimposedover the output signal U_(MESS1) of sensor 1. Outside of time intervalT1, T2, digital port DO of microcomputer 2 is connected to a relativelylow resistance R0 of, for example, 100 Ohms. Consequently, a maximuminterfering voltage of less than 100 mV, which can no longer causeinterference, is still present at A/D input 0 of microcomputer 2.

What is claimed is:
 1. An electronic device comprising:a sensor generating a first analog output signal on a sensor output line; and a microcomputer including a p lurality of A/D input lines, the sensor output line coupled to a first one of the plurality of A/D input lines, the microcomputer evaluating the first analog output signal and evaluating a second analog signal on a second one of the plurality of A/D input lines, the microcomputer further including an A/D converter converting the first analog output signal into a first digital signal and converting the second analog signal into a second digital signal, the first one of the plurality of A/D input lines having a first measurement interval, the second one of the plurality of A/D input lines having a second measurement interval, the second measurement interval being outside of the first measurement interval, wherein the first one of the plurality of A/D input lines is coupled to a first potential during the first measurement interval, and wherein the second one of the plurality of A/D input lines is coupled to a second potential during the second measurement interval.
 2. The electronic device according to claim 1, wherein the first one of the plurality of A/D input lines is further coupled to at least one digital port of the microcomputer.
 3. The electronic device according to claim 2, wherein each of the at least one digital port provides a first resistance during the first measurement interval and provides a second resistance less than the first resistance when outside of the first measurement interval.
 4. The electronic device according to claim 1, wherein the sensor output line is coupled to the first one of the plurality of A/D input lines via at least one voltage divider. 